The present invention relates to a flame arrester or firecheck device that is adapted to prevent a backfire from traveling upstream through a stream of flammable gas, and thus prevent unwanted fire or explosion that might otherwise be caused by the backfire.
A flame arrester is a passive device that permits the flow of gas, but prevents any external flame or backfire from xe2x80x9cflashing backxe2x80x9d through the flow of gas to the source of flammable material. If such a flashback is not prevented, the reservoir of flammable material would ignite, resulting in a destructive fire or explosion. Devices to prevent the passage of flame are critical to processes where flammable chemicals or vapors or handled, such as in petrochemical refineries, pipelines, sea-going tankers, combustion systems, hot water heaters, space heaters, and the like.
An example of an application requiring the use of a flame arrester is the vent opening normally provided on storage tanks containing oil, gas or other volatile substances, such vent opening being automatically operable to permit the escape of vapors when internal pressure exceeds a predetermined amount. Under some atmospheric conditions there is a tendency for the escaping vapors to saturate the atmosphere surrounding the tank to the point of inflammability, and in the event of accidental ignition when the vent is open, a flame arrester must be provided if the resulting combustion is to be prevented from traveling either slowly or explosively into the tank.
As another example, flame arresters are incorporated in combustible fuel lines and are used to protect the combustion system and its components from damage and to protect and safeguard operating personnel from injury resulting from deflagration and detonation caused by flashback. The flame arrester normally includes a burner screen which is intended to prevent the passage of flame from the system burner back to the gas-air mixture device.
Flame arrester elements are usually constructed of various open-structured metal configurations, such as perforated plates, bundles of tubes, screens, or beds of granules or fibers. The ability of any element to intervene and prevent the passage of fire, a first time, and over time, depends to a certain extent on the diameter and length of the array of its internal passages.
A difficulty which is commonly encountered is that most open-structured configurations which possess the required internal passage dimensions for successfully arresting a flame are able to survive the heat of the flame for only a limited time. When unwanted ignition takes place, there is normally a continued burning on the emergent face of the arrester over a relatively long period of time while the source of burning vapors is still present. Such extended exposure to the high temperature of the flame is normally destructive of the arrester, and therefore it is common practice to provide mechanical or other means responsive to the temperature of the arrester for closing a valve or otherwise shutting off the source of burning vapors. The burner screen in the arrester therefore acts only as a short term firecheck until more effective measures can be taken. However, the need for the mechanical or other means introduces additional expense, constant service and maintenance, and an additional array of moving parts which can malfunction.
A further difficulty is that, under certain ignition or detonation conditions, a rapidly developing shock wave will precede the flame front and can damage or completely destroy the open-structured configurations of the flame arrester elements before they have an opportunity to perform their flame arresting function.
It is an object of the present invention to provide a flame arrester which permits the normal flow of gas but produces substantially enhanced flame arresting properties.
It is another object of the invention to provide a flame arrester which is superior in its ability to resist melting when exposed to high temperature flames and to survive the force of shock waves encountered with unwanted ignitions.
It is a further object to provide a flame arrester which has no moving parts and is operative, without adjustment, when placed in any fuel or vent line.
It is a still further object of the invention to provide a flame arrester which is simple, durable, inexpensive to manufacture, easy to assemble, and relatively maintenance free.
This invention is based on the discovery that a flame can be prevented from flashing back in an upstream direction through a stream of flammable gas by placing in the stream an arrester comprising a contained layer or layers of nested ellipsoids formed from expanded metal sheets produced from a magnesium foil. It has been found that the expanded metal net magnesium alloy ellipsoids not only arrest the upstream travel of the flame but also with-stand the extreme heat of the flame and survive any shock wave that may be associated with the ignition of the flame.
The product of the present invention therefore is a flame arrester adapted for placement in a stream of flammable atmosphere for preventing an external flame at a downstream point in the stream from flashing back in an upstream direction to the source of the flammable atmosphere, said arrester comprising a contained layer of nested ellipsoids formed from expanded metal sheets made from magnesium alloy foil.
In one embodiment hereinafter described the flame arrester is placed in the vent pipe of a storage tank for a flammable substance. In another embodiment, the arrester is located in a conduit of a closed combustion system. In a further embodiment, the arrester is used to prevent the pilot or burner light of a hot water heater or space heater from igniting a fugitive flammable atmosphere caused by the accidental spillage of fuel in the vicinity of the heater.
The invention also comprises a method for preventing a supply of flammable atmosphere from being ignited by a flame burning externally of said atmosphere, comprising the step of placing the above-described arrester between said flame and said atmosphere.